Night Sky

[Irishman]

TheDude

Not really parallel, but all pointing in the same general direction. However, the light from stars travels far enough before it gets here that the light rays are essentially coherent - all aligned in parallel rays. This is process that is emulated to make laser coherent. They use tubes with mirrors to simulate a long travel distance to let only the coherent light out.

Just nitpicking here, but this is not exactly true. While it is true that the laser does use a tube with mirrors to only let coherent light out, the important part of a laser is embedded in the etymology of the word-Light Amplification by Stimulated Emission of Radiation. That is, the laser tube doesn’t just act as a orientation filter, but it also acts to amplify only the light that is oriented along the axis of the tube.

If one were simply to place a light source in a tube with mirrors on the ends, it would still act as a point source of light and not as a source of coherent light.

Righteo - I didn’t mean to imply that was the only significant part of laser generation.